Freeze tolerant fuel cell power plant with a direct contact heat exchanger

ABSTRACT

A power plant ( 10 ) includes at least one fuel cell ( 12 ), a coolant loop ( 18 ) including a freeze tolerant accumulator ( 22 ) for storing and separating a water immiscible fluid and water coolant, a direct contact heat exchanger ( 56 ) for mixing the water immiscible fluid and the water coolant within a mixing region ( 72 ) of the heat exchanger ( 56 ), a coolant pump ( 21 ) for circulating the coolant through the coolant loop ( 18 ), a radiator loop ( 84 ) for circulating the water immiscible fluid through the heat exchanger ( 56 ), a radiator ( 86 ) for removing heat from the coolant, and a direct contact heat exchanger by-pass system ( 200 ). The plant ( 10 ) utilizes the water immiscible fluid during steady-state operation to cool the fuel cell and during shut down of the plant to displace water from the fuel cell ( 12 ) to the freeze tolerant accumulator ( 22 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of prior application Ser. No.10/701,988, filed on Nov. 5, 2003, now U.S. Pat. No. 7,090,940.

TECHNICAL FIELD

The present invention relates to fuel cell power plants that are suitedfor usage in transportation vehicles, portable power plants, or asstationary power plants, and the invention especially relates to a fuelcell power plant that utilizes a direct contact heat exchanger thatfacilitates transfer of energy from a water coolant directly to a lowfreezing temperature water immiscible fluid during operation of theplant, wherein the water immiscible fluid also displaces a water coolantwithin fuel cells and a coolant loop of the plant during shut down ofthe plant.

BACKGROUND ART

Fuel cell power plants are well known and are commonly used to produceelectrical energy from hydrogen containing reducing fluid fuel andoxygen containing oxidant reactant streams to power electrical apparatussuch as stationary power plants and transportation vehicles. In fuelcell power plants of the prior art, it is known that product watergenerated by fuel cells of the plant is often utilized to provide waterfor plant systems such as fuel reformers as well as to humidify gaseousreactant streams. Such product water however presents significant freezerelated problems for the plant, especially during shut down and start upof the plant in sub-freezing ambient conditions.

Solutions to such freeze related problems are disclosed in U.S. Pat. No.6,528,194 that issued on Mar. 4, 2003 to Condit et al., and in U.S. Pat.No. 6,562,503 that issued on May 13, 2003 to Grasso et al., both ofwhich patents are entitled “Freeze Tolerant Fuel Cell Power Plant”, andboth of which are owned by the owner of all rights in the presentinvention. Those patents disclose the use of low freezing temperaturewater immiscible fluids as purge fluids, during a shut down and start upof the plant to displace water from key system components.

When the fuel cell power plant disclosed in those patents is shut downfor a short term shut down, displacement valves operate to control flowof the water coolant out of a fuel cell cooling coolant loop into afreeze tolerant, open tube accumulator, and to control flow of the waterimmiscible fluid into the coolant loop to displace the water coolant.For a long term shut down, the same procedure is undertaken to directthe water coolant into the accumulator; to direct the water immisciblefluid into the coolant loop to displace the water coolant; and, to thendrain the water immiscible fluid back into the accumulator.

To start up such a power plant after a long term shut down, the waterimmiscible fluid is first directed to pass from the accumulator througha heater or directly through operating fuel cells of the plant and intoa recycle line to flow through open tubes of the accumulator to melt thefrozen water coolant. Whenever fuel cells of the plant have attained adesired operating temperature and the water coolant within the freezetolerant accumulator has melted, flow of the water immiscible fluid outof the accumulator is terminated, and thawed water coolant is directedto flow through the coolant loop to cool the fuel cells and manage fuelcell product water. The freeze tolerant fuel cell power plant is then ina steady-state operation wherein the water coolant continues to cyclefrom the accumulator through the fuel cells and back to the accumulator,and the water immiscible fluid remains stored within the accumulator.The displacement or purge of the water coolant by the water immisciblefluid out of the fuel cells and coolant loop prevents mechanical damageto the plant by preventing the freezing of the water coolant during ashutdown and start up, until the water coolant is within the freezetolerant accumulator. Also, the low freezing temperature waterimmiscible fluid transfers heat from the fuel cells or an externalheater to melt frozen coolant water within the accumulator upon startup.

While the approach of these known solutions to freeze protection iseffective, nonetheless during steady-state operation of the plant, thewater immiscible fluid is not utilized, and remains inefficiently storedwithin the accumulator. Also, a large volume of fuel cell product waterand/or water coolant is required for efficient cooling of the plant, andsuch a large volume of water must be melted upon power plant start upafter an extended shut down in sub-freezing ambient conditions.Therefore, there is a need for a freeze tolerant fuel cell power plantthat efficiently utilizes a water immiscible purge fluid and thatminimizes a volume of water used in cooling the plant.

DISCLOSURE OF INVENTION

The invention is a freeze tolerant fuel cell power plant for generatingan electrical current from hydrogen containing reducing fluid fuel andoxygen containing oxidant reactant streams. The plant includes at leastone fuel cell including a coolant inlet and a coolant outlet fordirecting a coolant to flow through the fuel cell. A coolant loopincludes a freeze tolerant accumulator, such as an open tubeaccumulator, secured in fluid communication with the fuel cell coolantoutlet for storing and separating a water immiscible fluid and watercoolant; a direct contact heat exchanger secured in fluid communicationwith the accumulator and with the fuel cell coolant inlet; and, a fuelcell pump secured in fluid communication with a coolant passage of thecoolant loop for circulating coolant through the coolant loop.

The plant also includes a radiator loop including a radiator secured influid communication between a water immiscible fluid discharge and waterimmiscible fluid inlet of the direct contact heat exchanger for removingheat from the water immiscible fluid passing through the radiator; aradiator pump secured to the radiator loop for circulating the waterimmiscible fluid through the radiator and direct contact heat exchanger;and, a water immiscible fluid reservoir secured in fluid communicationwith the radiator and the direct contact heat exchanger for supplyingthe water immiscible fluid to the radiator loop and coolant loop.

The plant also includes a direct contact heat exchanger by-pass systemfor directing flow of the coolant directly from the coolant loop throughthe radiator and back to the coolant loop without passing through thedirect contact heat exchanger. The by-pass system also restricts flow ofthe water immiscible fluid through the radiator and coolant loop. Thedirect contact heat exchanger by-pass system facilitates usage of thewater coolant whenever the plant experiences a high heat rejectiondemand, such as whenever the ambient temperatures are in excess of 30degrees Celsius (“° C.”). Water has a higher thermal rejectioncapability than the water immiscible fluids appropriate for coolants inthe power plant. Therefore, the by-pass system provides for use of wateras the heat rejection coolant during periods of high heat rejectionrequirements, while isolating the water immiscible fluid coolant out ofthe coolant loop.

Operation control valves for operating the plant include: an accumulatorfeed valve secured in fluid communication with the accumulator forselectively directing the coolant within the coolant loop to flow intoeither a water inlet of the accumulator or a water immiscible fluidinlet of the accumulator; an accumulator discharge valve for selectivelydirecting flow from the accumulator into the coolant loop from anaccumulator water outlet, from an accumulator water immiscible fluidoutlet, or from an accumulator water immiscible fluid discharge header;a direct contact heat exchanger feed valve for selectively directing thecoolant to flow into a mixing inlet of the direct contact heat exchangeror to by-pass the direct contact heat exchanger. A water immisciblefluid reservoir feed valve may also be secured to the radiator loop forselectively directing flow of the water immiscible fluid from theradiator into the reservoir or into the direct contact heat exchanger.Direct contact heat exchanger by-pass valves selectively direct flow ofthe water coolant from the coolant loop to the radiator and back to thecoolant loop by-passing the direct contact heat exchanger. Also, waterimmiscible fluid isolation valves restrict flow of the water immisciblefluid coolant from the direct contact heat exchanger, radiator loop andwater immiscible fluid reservoir into the coolant loop whenever theby-pass valves direct flow of the water coolant directly through theradiator by-passing the direct contact heat exchanger.

In a preferred embodiment wherein a portion of the fuel cell productwater passes into the coolant loop, such as through a porous watertransport plate adjacent to the fuel cell, the accumulator may include awater overflow discharge line to direct excess product water out of theplant.

By providing for direct contact between the water coolant and the waterimmiscible fluid within the direct contact heat exchanger, the powerplant of the present invention facilitates efficient usage of a lowfreezing temperature water immiscible fluid in both directly cooling theplant and purging water coolant from fuel cells of the plant, while alsominimizing a volume of water coolant necessary to operate the plant.

Accordingly, it is a general purpose of the present invention to providea freeze tolerant fuel cell power plant with a direct contact heatexchanger that overcomes deficiencies of the prior art.

It is a more specific purpose to provide a freeze tolerant fuel cellpower plant with a direct contact heat exchanger that provides for usageof a water immiscible fluid in cooling the plant and purging water froma fuel cell of the plant during shut down of the plant.

These and other purposes and advantages of the present passive watermanagement system for a fuel cell power plant will become more readilyapparent when the following description is read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a preferred embodiment of afreeze tolerant fuel cell power plant with a direct contact heatexchanger constructed in accordance with the present invention.

FIG. 2 is the schematic representation of the FIG. 1 embodiment of thefreeze tolerant fuel cell power plant showing a direct contact heatexchanger by-pass system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in detail, a freeze tolerant fuel cell powerplant with a direct contact heat exchanger is shown in FIG. 1, and isgenerally designated by the reference numeral 10. The plant 10 includesat least one fuel cell 12 for generating electrical current fromhydrogen containing reducing fluid and oxygen containing oxidantreactant streams as is known in the art. The fuel cell includes acoolant inlet 14 and a coolant outlet 16 for directing flow of acoolant, such as a water coolant, through the fuel cell 12. A coolantloop 18 provides for circulating the coolant from the coolant outlet 16to the coolant inlet 14, and includes a coolant passage 20 secured influid communication between the coolant outlet 16 and coolant inlet 14,and a coolant circulating means secured to the coolant passage 20, suchas a first coolant pump 21. The coolant loop 18 also includes a freezetolerant accumulator means for storing and separating the water coolantand a water immiscible fluid in such a manner that the accumulator meansis not damaged by freezing of the water coolant. An exemplary freezetolerant accumulator means 22 is an open tube accumulator shownschematically in FIG. 1, and also described in the aforesaid U.S. Pat.6,562,503.

The accumulator 22 includes a water immiscible fluid region 24 and awater region 26 that may be separated by a porous layer, such as asponge or membrane 28. The sponge 28 facilitates separation of watercoolant and water immiscible fluid within the accumulator 22 whilepermitting movement of any of the water coolant and/or water immisciblefluid through the sponge 28 during a separation of the liquids basedupon their differing densities. The accumulator 22 also includes a waterinlet 30 secured in fluid communication with the water region 26 of theaccumulator 22 and an accumulator water outlet 32 that is also securedin fluid communication with the water region 26. A water outlet valve 33is secured in fluid communication with the accumulator water outlet 32and accumulator outlet line 37. An accumulator water immiscible fluidoutlet 34 and water immiscible fluid outlet valve 35 is secured to thewater immiscible fluid region 24 of the accumulator 22 for selectivelydirecting flow of the water immiscible fluid out of the accumulator 22.The accumulator 22 also includes a plurality of tubes 36A, 36B, 36C, 36Dextending through the water region 26 of the accumulator 22 and betweena water immiscible fluid inlet header 38 and a water immiscible fluiddischarge header 40. A water immiscible fluid inlet 42 is secured influid communication with the accumulator inlet header 38 for directingflow of the water immiscible fluid into the inlet header 38 and throughthe tubes 36A, 36B, 36C, 36D to the accumulator discharge header 40. Theaccumulator 22 may also include a water overflow discharge line 44 andwater discharge vent valve 46.

An accumulator feed valve means 48 is secured in fluid communicationwith the coolant passage 20 for selectively controlling flow of thecoolant from the coolant passage 20 either into the water inlet 30 orthe water immiscible fluid inlet 42 of the accumulator 22. Theaccumulator feed valve means 48, and any “valve means” described herein,include a described form of the valve, such as a common accumulator feedthree-way valve 48 shown in FIG. 1 secured to the coolant passage 20, orany other structure or structures known in the art and capable ofperforming the described flow control functions, such as two separatevalves (not shown) secured in fluid communication with, and adjacent to,the water inlet 30 and water immiscible fluid inlet 42 of theaccumulator 22.

In a particular operation of the plant 10, the accumulator feed valvemeans 48 may direct water immiscible fluid to pass into the accumulator22 through the water inlet 30. In such circumstances, the accumulatorsponge 28 permits the water immiscible fluid to pass from the waterregion 22 of the accumulator 22 through the sponge 28 into the waterimmiscible region 24.

An accumulator discharge valve means 50 is secured in fluidcommunication with the accumulator water outlet 32 and accumulatoroutlet line 37 for directing the water coolant or the water immisciblefluid from the accumulator 22 along the coolant loop 18 within a firstextension 52 of the coolant passage 20. The accumulator discharge valvemeans may include the water immiscible fluid outlet valve 35, wateroutlet valve 33 and outlet line 37 as the separate components shown inFIG. 1 along with an accumulator discharge three-way valve 50 secured tothe accumulator outlet line 37 and a water immiscible fluid flow throughheader line 51 secured to the discharge header 40, or the accumulatordischarge valve means 50 may be an integral unit combining thosecomponents. A direct contact heat exchanger feed valve means 54 issecured to the first extension 52 of the coolant passage 20 and in fluidcommunication with a mixing inlet 70 of a direct contact heat exchanger56 for selectively directing the water coolant to flow into the inlet 70(also referred to herein as a “water coolant inlet 70”) of the heatexchanger 56 from the accumulator 22. Alternatively, the direct contactheat exchanger feed valve means 54 may direct the water coolant toby-pass the heat exchanger 56 during a shut down or start up process viaa by-pass coolant passage 58 secured between the first extension 52 ofthe coolant passage 20 and the coolant inlet 14 of the fuel cell 12.

The direct contact heat exchanger 56 is utilized to transfer waste heatfrom the fuel cell 12 to the ambient environment. The water coolant,circulating through the fuel cell 12, mixes with a water immisciblefluid within the direct contact heat exchanger 56 and transfers thethermal energy from the water coolant to the water immiscible fluid. Thetwo fluids then separate within the direct contact heat exchanger 56,and the water coolant is circulated back through the fuel cell 12 whilethe water immiscible fluid is circulated through a radiator loop 84 thatdischarges the thermal energy to ambient.

The direct contact heat exchanger 56 has three regions: a mixing region72, a separation region 74, and a water region 76. The coolant waterflows from the heat exchanger 56 through a second extension 81 of thecoolant passage 20, through the coolant inlet 14, and into the fuel cell12. The direct contact heat exchanger feed valve means 54 may be in theform of a two-way valve 54 secured between the coolant passage 20 andthe mixing inlet 70 along with an additional two-way by-pass valve 83secured to the by-pass coolant passage 58. Or, the direct contact heatexchanger feed valve means 54 may be in the form of a three-way valve(not shown) secured between the coolant passage 20 and the mixing inlet70 for selectively directing the coolant to flow into the mixing region72 of the direct contact heat exchanger 56 or to flow through theby-pass coolant passage 58.

The plant 10 also includes the radiator loop 84 including a radiator 86secured in fluid communication between a water immiscible fluiddischarge 91 and a water immiscible fluid inlet 90 of the direct contactheat exchanger 56 for removing heat from the water immiscible fluidpassing through the radiator 86; a radiator pump 92 secured to theradiator loop 84 for circulating the water immiscible fluid through theradiator 86 and direct contact heat exchanger 56; a water immisciblefluid reservoir 94 secured in fluid communication with the radiator 86and the direct contact heat exchanger 56 for supplying the waterimmiscible fluid to the radiator loop 84 and coolant loop 18; and, awater immiscible fluid reservoir feed valve means 96 that may be securedin fluid communication between the radiator 86 and mixing region 72 ofthe heat exchanger 56 for selectively controlling flow of the waterimmiscible fluid to circulate within the radiator loop 84 from theradiator 86 or to feed the water immiscible fluid reservoir 94. Theradiator 86 and reservoir 94 may be secured in fluid communication witha water immiscible fluid inlet line 89 leading to the water immisciblefluid inlet 90. The radiator may include a fan 87 such as known in anautomotive radiator and fan.

The freeze tolerant accumulator means 22 and direct contact heatexchanger means 56 described above are constructed so that the waterimmiscible fluid is less dense than the water coolant. Therefore, duringa steady-state operation, the water coolant descends to the water region26 of the accumulator 22 and to the water region 76 of the heatexchanger 56. Meanwhile, the water immiscible fluid remains primarilywithin the separation region 74 of the heat exchanger 56 and within thereservoir 94. However, one skilled in the art could readily construct afreeze tolerant accumulator means 22 and direct contact heat exchangermeans 56 that utilizes a water immiscible fluid that is more dense thanthe water coolant.

As shown in FIG. 2, the freeze tolerant fuel cell power plant 10 alsoincludes a direct contact heat exchanger by-pass system means 200 fordirecting flow of the coolant from the coolant loop 18 through theradiator 86 and back to the coolant loop 18 without passing through thedirect contact heat exchanger 56. The by-pass system 200 includes aby-pass feed line 201 secured in fluid communication between the coolantloop 18 and the radiator 86, such as secured between the coolant passage20 and the water immiscible fluid discharge line 88 that extends betweenthe direct contact heat exchanger 56 and the radiator 86. The by-passsystem 200 also includes a by-pass return line 202 secured in fluidcommunication between the radiator 86 and the coolant loop 20, such assecured between the water immiscible fluid inlet line 89 and the coolantpassage 20.

The by-pass system 200 also includes by-pass valve means for directingthe coolant to flow from the coolant loop 18 through the by-pass feedline 201 to the radiator 86 and from the radiator back through theby-pass return line 202 to the coolant loop 18 without passing throughthe direct contact heat exchanger 56. Any valves or flow controlapparatus known in the art that can achieve the described function ofthe by-pass valve means are appropriate for the present invention.Exemplary by-pass valve means shown in FIG. 2 include a coolant loopby-pass feed valve 204 that interrupts flow of the coolant through thecoolant passage 20 of the coolant loop so that the coolant flows intothe by-pass feed line 201. The by-pass valve means also includes anyvalve that prohibits flow of the coolant from the coolant loop 18 intothe direct contact heat exchanger 56, such as the direct contact heatexchanger feed valve 54 and two-way by-pass or direct contact heatexchanger by-pass valve 83 secured to the first extension 52 of thecoolant passage 20 (shown in both FIGS. 1 and 2). An additionalexemplary by-pass valve is a radiator loop by-pass valve 206 secured todirect the coolant being discharged out of the radiator 86 into theby-pass return line 202, such as being secured to the water immisciblefluid inlet line 89 that extends between the radiator 86 and the directcontact heat exchanger 56. The radiator loop by-pass valve 206 may be athree-way valve known in the art for selectively directing flow of thecoolant from the radiator 86 into either the by-pass return line 202 orthe water immiscible fluid inlet line 89 and for restricting flow intoor from the non-selected source of flow.

The by-pass system 200 also includes water immiscible fluid isolationvalve means for restricting flow of the water immiscible fluid from thedirect contact heat exchanger 56, water immiscible fluid reservoir 94and radiator loop 84 into the coolant loop 18 whenever the by-pass valvemeans are directing flow of the coolant directly from the coolant loop18 to the radiator 86 and back to the coolant loop 18 by-passing thedirect contact heat exchanger 56. Any valves or flow control apparatusknown in the art that can achieve that described function areappropriate for the present invention. Exemplary water immiscible fluidisolation valve means shown in FIG. 2 include a direct contact heatexchanger discharge valve 208 secured in fluid communication with anoutlet, such as the water outlet 85, of the direct contact heatexchanger 54. An additional water immiscible fluid isolation valve meansshown in FIG. 2 is a radiator inlet valve 210 secured in fluidcommunication between the by-pass feed line 201, the water immisciblefluid discharge line 88 extending between the direct contact heatexchanger 56 and the radiator 86 and a radiator inlet 212, as shown inFIG. 2. The radiator inlet valve 210 may be a three-way valve known inthe art, or any other flow control valve or apparatus that mayselectively direct flow from either the by-pass feed line 201 or thedirect contact heat exchanger 56 into the radiator 86 and that alsorestricts flow into or from the non-selected source of flow.

During steady-state operation of the plant 10, the coolant pump 21circulates the water coolant from the fuel cell 12, through the coolantoutlet 16, through the coolant passage 20, through the accumulator feedvalve 48, through the freeze tolerant accumulator water inlet 30,through the accumulator water outlet 32, and through the accumulatordischarge valve 50. From there, the water coolant passes through thefirst extension 52 of the coolant passage 20, through the direct contactheat exchanger feed valve 54, through the mixing inlet 70 of the directcontact heat exchanger 56, and into the mixing region 72 of the heatexchanger 56. The water immiscible fluid inlet 90 of the direct contactheat exchanger 56 simultaneously directs flow of the water immisciblefluid from the radiator loop 84 into the mixing region 72 of the directcontact heat exchanger 56 to mix directly with the water coolant so thatthermal energy from the water coolant is transferred to the waterimmiscible fluid. Based upon differing densities, the water coolant andwater immiscible fluid within the heat exchanger 56 separate. The watercoolant descends to the water region 76 of the heat exchanger 56, andthe water immiscible fluid moves from the mixing region 72 to theseparation region 74 of the heat exchanger 56. The water coolant withinthe water region 76 of the heat exchanger 56 then flows through a watercoolant outlet 85 of the heat exchanger 56 into the second extension 81of the coolant passage 20 back into the coolant loop 18 and into thefuel cell 12 through the coolant inlet 14. Meanwhile, the heated waterimmiscible fluid flows from the water immiscible fluid discharge 91defined in the separation region 74 of the radiator loop 86 into a waterimmiscible fluid discharge line 88 of the radiator loop 84 through theradiator 86 and then back into the heat exchanger 56 to remove heatthrough the radiator 86.

If the power plant 10 requires a high rate of heat rejection, such as ifambient temperatures exceed 30° C., the direct contact heat exchangerby-pass system 200 may be operated to enhance heat rejection by theplant 10. Operation of the system includes controlling the coolant loopby-pass valve 204 to direct flow of the coolant from the coolant loop 18into the by-pass feed line 201; controlling the radiator inlet valve 210to direct flow of the coolant from the by-pass feed line 201 into theradiator inlet 212; and controlling the radiator loop by-pass valve 206to direct flow of the coolant from the radiator 86 through the by-passreturn line 202 to the coolant loop 18 and to restrict flow of the waterimmiscible fluid from the reservoir 94 into the by-pass return line 202.Additionally, the radiator inlet valve 210 is controlled to prohibitflow of the water immiscible fluid from the direct contact heatexchanger 56 into the radiator 86, while the direct contact heatexchanger valve 208 is controlled to prohibit flow of coolant out of thedirect contact heat exchanger 56 into the second extension 81 of thecoolant passage 20 of the coolant loop 18. Also, the direct contact heatexchanger feed valve 54 is controlled to prohibit flow of coolant intothe direct contact heat exchanger 56 and the two-way by-pass or directcontact heat exchanger by-pass valve 83 is controlled to direct flow ofthe coolant through the fuel cell 12. During use of the direct contactheat exchanger by-pass system 200, the radiator pump 92 is turned off.

The direct contact heat exchanger by-pass system 200 thereby directsflow of the coolant from the coolant passage 20 through the by-pass feedline 201, radiator 86, by-pass return line 202, into and through theaccumulator 22 wherein any water immiscible fluid is separated into thewater immiscible fluid region 24 of the accumulator. Water coolant isthen directed through the water outlet valve 33 from the accumulator 22into the first extension 52 of the coolant passage 20, through thedirect contact heat exchanger by-pass valve 83 and through the secondextension 81 of the coolant passage 20 into the coolant inlet 14, thenthrough the fuel cell 12 and coolant outlet 16, coolant pump 21, andback into the by-pass feed line 201.

The direct contact heat exchanger by-pass system 200 thereby providesfor usage of the water coolant to reject heat from the fuel cell 12,instead of the water immiscible fluid coolant. The water coolant has ahigher thermal rejection capacity than the water immiscible fluid, andtherefore provides for more efficient heat rejection. Additionally, useof the by-pass system 200 only requires use of the coolant pump 21 anddoes not require usage of the radiator pump 92, thereby providingfurther efficiency in operation of the plant 10.

To stop usage of the direct contact heat exchanger by-pass system 200,the coolant loop by-pass feed valve 204 is controlled to direct flow ofthe coolant through the coolant passage instead of into the by-pass feedline 201; the radiator inlet valve 210 is controlled to stop flow of thecoolant from the by-pass feed line 201 into the radiator and instead todirect flow of the water immiscible fluid from the heat exchanger 56into the radiator 86; the radiator loop by-pass valve 206 is controlledto direct flow of the coolant flowing out of the radiator 86 into thewater immiscible fluid inlet line 89 instead of into the by-pass returnline 202; the direct contact heat exchanger feed valve 54 is controlledto direct the coolant into the heat exchanger 56; the direct contactheat exchanger by-pass valve 83 is controlled to prohibit the coolantfrom by-passing the direct contact heat exchanger 56; the direct contactheat exchanger discharge valve 208 is controlled to direct flow of thecoolant from the heat exchanger 56 into the second extension 81 of thecoolant passage; and the radiator pump 92 is turned on, therebyreturning the plant to steady-state operation.

During a shut down of the plant in sub-freezing ambient conditions, anelectrical load (not shown) is disconnected from the fuel cell 12, andthe water immiscible fluid outlet valve 35 secured in fluidcommunication with the accumulator water immiscible fluid outlet 34 andthe accumulator discharge valve means 50 are controlled to direct waterimmiscible fluid stored within the accumulator 22 into the coolant loop18 while the direct contact heat exchanger feed valve 54 is controlledto direct the flow of the water coolant and water immiscible fluid toby-pass the direct contact heat exchanger 56 through the by-pass coolantpassage 58. The by-pass feed valve 204, radiator inlet valve 210, andradiator loop by-pass valve 206 are also controlled to direct flow ofthe water immiscible fluid through the by-pass feed line 201 and by-passreturn line 202 for a short duration to purge water out of the feed andreturn lines 201, 202 with the water immiscible fluid. The accumulatorwater outlet valve 33 is also controlled to terminate flow of water outof the accumulator 22. If excess fuel cell 12 product water is passingfrom the accumulator 22 to other plant systems (not shown) through theaccumulator's water discharge vent valve 46, the valve 46 is controlledto terminate flow.

The coolant pump 21 will then direct all of the water coolant into theaccumulator 22 which provides for separation of the water coolant andwater immiscible fluid based upon their differing densities until thewater immiscible fluid has purged the water coolant from the fuel cell12 and coolant passage 20 and into the accumulator 22. The directcontact heat exchanger feed valve 54 is then controlled to direct waterimmiscible fluid flow back into the heat exchanger 56 so that the waterimmiscible fluid from the accumulator 22 and the water immiscible fluidreservoir 94 flow through and fill the fuel cell 12 and the coolant loop18, including the direct contact heat exchanger 56 and accumulator 22thereby displacing the water in the direct contact heat exchanger 56.The first coolant pump 21 and radiator pump 92 are then shut down.

In starting up the power plant 10 from a sub-freezing shut down whereinthe water coolant within the accumulator 22 has frozen, first, reactantstreams are passed through the fuel cell 12 as the electrical load (notshown) is connected to the cell 12. This operation of the fuel cell 12generates heat and electrical power. The heat generated by the fuel cell12 is absorbed by circulating the water immiscible fluid through thefuel cell 12. The heated water immiscible fluid may be used to melt anyice in the accumulator 22. An electric heater (not shown) may also beplaced within the coolant loop 18 or accumulator 22 to further heat thewater immiscible fluid during start up from a sub-freezing condition.During such a start up, only the coolant pump 21 operates and theaccumulator discharge valve means 50 is controlled to direct flow of thewater immiscible fluid from the accumulator 22 and through the fuel cell12 to heat the fluid while the direct contact heat exchanger feed valve54 is controlled to direct the heated water immiscible fluid to by-passthe heat exchanger 56. The accumulator feed valve 48 is controlled todirect the heated water immiscible fluid to flow into the waterimmiscible fluid inlet 42 and inlet header 38 of the accumulator 22. Theheated water immiscible fluid then flows through the tubes 36A, 36B,36C, 36D of the accumulator 22 that pass through the frozen watercoolant to melt the frozen water coolant.

Whenever the water coolant is melted, the radiator pump 92 is started,the direct contact heat exchanger feed valve 54 is controlled to directthe flow of the water immiscible fluid into the heat exchanger 56, andthe water immiscible fluid reservoir feed valve means 96 is controlledto direct flow of the water immiscible fluid into the reservoir 94. Thewater immiscible fluid is thereby directed out of the fuel cell 12. Whenthe volume of water immiscible fluid remaining within the accumulator 22declines to a pre-determined storage volume, the accumulator dischargevalve 50 is controlled to direct flow of the melted water coolant fromthe accumulator 22 to the direct contact heat exchanger 56, and theaccumulator feed valve 48 is controlled to direct flow of the watercoolant into the water inlet 30 of the accumulator 22. The accumulatorwater outlet valve 33 of the accumulator discharge valve means 50 isalso controlled to direct flow of the water coolant from the accumulator22 into the coolant loop. As coolant water displaces the waterimmiscible fluid from the fuel cell 12, the water immiscible fluidreservoir feed valve means 96 is controlled to direct flow so that thewater immiscible fluid flows from the radiator 86 of the radiator loop84 into the direct contact heat exchanger 56. Then, the accumulator'swater discharge vent valve 46 is opened. The power plant 10 has beenreturned to a steady-state operation.

In operation of the freeze tolerant fuel cell power plant with a directcontact heat exchanger 10, the valves described above are controlled bya controller means known in the art for controlling valves. Suchcontroller means actuate valves in response to sensed information. Inparticular, the controller means controls the accumulator feed valvemeans 48 for selectively directing the coolant within the coolant loop18 to flow into either a water inlet 30 of the accumulator 22 or a waterimmiscible fluid inlet 42 of the accumulator 22; controls theaccumulator discharge valve means 50 for selectively directing flow ofthe coolant from the accumulator 22 into the coolant loop 18 from theaccumulator water outlet 32, from the accumulator water immiscible fluidoutlet 34, or from the accumulator water immiscible fluid dischargeheader 40; controls the direct contact heat exchanger feed valve means54 for selectively directing the coolant to flow into a mixing inlet 70of the contact heat exchanger 56 or to by-pass the direct contact heatexchanger 56 via the by-pass coolant passage 58; and, controls the waterimmiscible fluid reservoir feed valve means 96 for selectively directingthe coolant into the reservoir 94 or into the mixing region 72 of theheat exchanger 56. The controller means also controls the direct contactheat exchanger by-pass valve means 204, 54, 83, 206 for selectivelydirecting flow of the coolant from the coolant loop 18 to the radiator86 and back to the coolant loop 18 by-passing the direct contact heatexchanger 56, or for directing flow of the coolant through the coolantloop 18 and direct contact heat exchanger 56; and controls the waterimmiscible fluid isolation valve means 208, 210 for selectivelyprohibiting flow of the water immiscible fluid from the direct contactheat exchanger 56, water immiscible fluid reservoir 94, and radiatorloop 84 into the coolant loop 18 whenever the by-pass valve means 204,54, 206 direct flow of the coolant directly from the coolant loop 18through the radiator 86 and back to the coolant loop 18. The controllermeans could actuate the accumulator feed valve means 48, the accumulatordischarge valve means 50, the direct contact heat exchanger feed valvemeans 54, and the water immiscible fluid reservoir feed valve means 96through well known mechanisms, including manual valve controls,electro-mechanical actuators, electro-hydraulic actuators, etc. Theaforesaid valve means 48, 50, 54, 96 may also be combined or coordinatedas an integral operational control valve means for performing thedescribed functions of the present invention.

A first preferred water immiscible fluid is selected from the groupconsisting of silicon-containing fluids such as: silicones, siliconecopolymers, substituted silicones, siloxanes, polysiloxanes, substitutedsiloxanes or polysiloxanes and mixtures thereof that have a freezingtemperature that is at least as low as minus twenty (−20) degreesCelsius (“° C.”) and that are not miscible with water. Suitablesilicon-containing fluids are dimethyl fluids, which are available fromthe GE SILICONES Company of Waterford N.Y., U.S.A. and sold under thedesignation “SF96 series” or from the DOW CHEMICAL Midland, Mich.,U.S.A. and sold under the designation of “Syltherm HF” or “SylthermXLT”. Suitable polysiloxane fluids are available from the aforesaid GESILICONES Company and sold under the designation of “SF1488 series” or“SFxx88 series”. These fluids are copolymers of polydimethylsiloxane anda polyethylene oxide.

A second preferred water immiscible fluid is selected from the groupconsisting of perfluorocarbons, hydrofluoroethers, and mixtures thereofthat have a freezing temperature that is at least as low as minus twenty(−20) degrees Celsius (“° C.”) and that are not miscible with water.Suitable perfluorocarbons are perfluoroalkanes, perfluorotrialkylamineand perfluorotributylamine, which are available from the 3M Company ofSt. Paul, Minn., U.S.A. and are sold under the designations of “GradesFC-77, FC-3283, and FC-40” respectively. A suitable hydrofluoroether issold under the designation “Grade HFE-7500”. The aforesaidperfluorocarbons are available from the 3M Company under the trademark“FLUORINERT PFC”, and the suitable hydrofluoroethers are also availablefrom the aforesaid 3M Company under the trademark “NOVEC HFE”.

A third preferred water immiscible fluid is selected from the groupconsisting of alkanes, alkenes, alkynes, and mixtures thereof that havea freezing temperature that is at least as low as −20° C. and that arenot miscible with water. Suitable alkanes include Heptane (C₇H₁₆,melting point −91° C.), Octane (C₈H₁₈, melting point −57° C.), Nonane(C₉H₂₀ melting point −54° C.), and Decane (C₁₀H₂₂, melting point −30°C.). Suitable alkenes included Cyclohexene (C₆H₁₀, melting point −103°C.), Heptene (C₇H₁₄, melting point −119° C.), Cycloheptene (C₇H₁₂,melting point −56° C.), Octene (C₈H₁₂, melting point −102° C.),Cylooctene (cis) (C₈H₁₄, melting point −12° C.), and Cylooctene (trans)(C₈H₁₄, melting point −59° C.). Suitable Alkynes include 2-Octyne(C₈H₁₄, melting point −62° C.), and 1-Decene (C₁₀H₁₈, melting point −36°C.). Many other alkanes, alkenes, alkynes having six or more carbonatoms, or mixtures thereof that have a freezing temperature that is atleast as low as −20° C. and that are not miscible with water will alsomake a suitable water immiscible fluid, such as for example those havingmultiple double and/or triple bonds. All such alkanes, alkenes, andalkynes and mixtures thereof are available from large chemicalsuppliers, such as the Aldrich Company, of Milwaukee, Wis., U.S.A.

The preferred water immiscible fluids may also have surface tensionsthat are less than or equal to 35 dynes per square centimeter(“dynes/cm”) and most preferably less than or equal to 20 dynes persquare centimeter. The preferred water immiscible fluids also may have asolubility in water of less than 0.1 percent.

In a preferred embodiment wherein the fuel cell product water passesinto the coolant loop 18, such as through a porous water transport plate(not shown) adjacent to the fuel cell 12, the fuel cell 12 product watermay be directed from the accumulator 22 through the water overflowdischarge line 44 and discharge vent valve 46 to direct the excessproduct water to other plant systems (not shown) or out of the plant 10.

It can be seen that the freeze tolerant fuel cell power plant with adirect contact heat exchanger 10 of the present invention efficientlyutilizes a low freezing temperature water immiscible purge fluid todisplace coolant water out of the fuel cell 12 to the freeze tolerantaccumulator 22 while minimizing a volume of water used in cooling theplant 10. Furthermore, during steady-state operation, most of the waterimmiscible fluid is utilized within the power plant 10, instead of beingstored within the accumulator 22. Consequently, the water immisciblefluid used during steady-state operation helps cool the plant 10 andreduces a total volume of water coolant needed to cool the plant 10.

The patents referred to above are hereby incorporated herein byreference.

While the present invention has been described with respect to aparticular construction of a freeze tolerant fuel cell power plant witha direct contact heat exchanger 10, it is to be understood that theinvention is not to be limited to the described or illustratedembodiments. Accordingly, reference should be made to the followingclaims rather than the foregoing description to determine the scope ofthe invention.

1. A freeze tolerant fuel cell power plant for generating an electricalcurrent from hydrogen containing reducing fluid fuel and oxygencontaining oxidant reactant streams, the plant comprising: a. at leastone fuel cell (12) including a coolant inlet (14) and a coolant outlet(16) for directing a water immiscible fluid and a water component toflow through the fuel cell (12); b. a coolant loop (18) including afreeze tolerant accumulator means (22) secured in fluid communicationwith the fuel cell coolant outlet (16) for storing and separating thewater immiscible fluid and the water component, a direct contact heatexchanger (56) secured in fluid communication with the accumulator means(22) and the fuel cell coolant inlet (14), and a coolant circulatingmeans (21) secured in fluid communication with a coolant passage (20) ofthe coolant loop (18) for circulating the water immiscible fluid and thewater component through the coolant loop (18); c. a radiator loop (84)including a radiator (86) secured in fluid communication between a waterimmiscible fluid discharge (91) and water immiscible fluid inlet (90) ofthe direct contact heat exchanger (56) that removes heat from the waterimmiscible fluid passing through the radiator (86), and a radiator pump(92) secured to the radiator loop (84) for circulating the waterimmiscible fluid through the radiator (86) and direct contact heatexchanger (56); and, d. a direct contact heat exchanger by-pass systemmeans (200) for directing flow of the water component from the coolantloop (18) directly through the radiator (86) and back to the coolantloop (18) by-passing the direct contact heat exchanger (56).
 2. Thefreeze tolerant fuel cell power plant (10) of claim 1, wherein thedirect contact heat exchanger by-pass system means (200) comprisesby-pass valve means for directing the water component to flow from thecoolant loop (18) through a by-pass feed line (201) to the radiator (86)and from the radiator (86) through a by-pass return line (202) back tothe coolant loop (18) by-passing the direct contact heat exchanger (56).3. The freeze tolerant fuel cell power plant (10) of claim 2, whereinthe direct contact heat exchanger by-pass system means (200) furthercomprises water immiscible fluid isolation valve means for restrictingflow of the water immiscible fluid from the direct contact heatexchanger (56) and the radiator loop (84) into the coolant loop (18)whenever the by-pass valve means are directing flow of the watercomponent directly from the coolant loop (18) to the radiator (86) andback to the coolant loop (18) by-passing the direct contact heatexchanger (56).
 4. The freeze tolerant fuel cell power plant (10) ofclaim 2, wherein the by-pass valve means comprises a coolant loopby-pass feed valve (204) for selectively directing flow of the watercomponent from the coolant loop (18) into the by-pass feed line (201), adirect contact heat exchanger feed valve (54) and direct contact heatexchanger by-pass valve (83) for selectively prohibiting flow of thewater component into the direct contact heat exchanger (56), and aradiator loop by-pass valve (206) for selectively directing the watercomponent discharged out of the radiator (86) into the by-pass returnline (202).
 5. The freeze tolerant fuel cell power plant (10) of claim3, wherein the water immiscible fluid isolation valve means comprises adirect contact heat exchanger discharge valve (208) secured in fluidcommunication with an outlet of the direct contact heat exchanger (56)for selectively prohibiting flow of the water component out of the heatexchanger (56), and a radiator inlet valve (210) secured in fluidcommunication between the by-pass feed line (201), the direct contactheat exchanger (56) and the radiator (86) for selectively directing flowfrom either the by-pass feed line (201) or the heat exchanger (56) intothe radiator (86).
 6. The freeze tolerant fuel cell power plant (10) ofclaim 1, wherein the water immiscible fluid is selected from the groupconsisting of silicones, silicone copolymers, substituted silicones,siloxanes, polysiloxanes, substituted siloxanes or polysiloxanes andmixtures thereof.
 7. The freeze tolerant fuel cell power plant (10) ofclaim 1, wherein the water immiscible fluid is selected from the groupconsisting of perfluorocarbons, hydrofluoroethers and mixtures thereof.8. The freeze tolerant fuel cell power plant (10) of claim 1, whereinthe water immiscible fluid is selected from the group consisting ofalkanes, alkenes, alkynes having six or more carbon atoms and mixturesthereof.
 9. The freeze tolerant fuel cell power plant (10) of claim 1,wherein the water immiscible fluid has a freezing temperature equal toor less than minus twenty degrees Celsius, has a surface tension of lessthan or equal to 35 dynes/cm, and has a solubility in water of less than0.1 percent.
 10. The freeze tolerant fuel cell power plant (10) of claim1, wherein the water immiscible fluid has a freezing temperature equalto or less than minus twenty degrees Celsius, has a surface tension ofless than or equal to 20 dynes/cm, and has a solubility in water of lessthan 0.1 percent.
 11. A method of operating a freeze tolerant fuel cellpower plant (10), the power plant (10) including at least one fuel cell(12) having a coolant inlet (14) and a coolant outlet (16) for directinga water immiscible fluid and a water component to flow through the fuelcell (12), a coolant loop (18) including a freeze tolerant accumulator(22) secured in fluid communication with the fuel cell coolant outlet(16) for storing and separating the water immiscible fluid and the watercomponent, and a coolant pump (21) secured in fluid communication with acoolant passage (20) of the coolant loop (18) for circulating the watercomponent and water immiscible fluid through the coolant loop (18), themethod comprising the steps of: a. securing a direct contact heatexchanger (56) in fluid communication with the accumulator (22) and thefuel cell coolant inlet (14); b. providing a radiator loop (84)including a radiator (86) secured in fluid communication between a waterimmiscible fluid discharge (91) and water immiscible fluid inlet (90) ofthe direct contact heat exchanger (56) that removes heat from the waterimmiscible fluid passing through the radiator (86), a radiator pump (92)secured to the radiator loop (84) for circulating the water immisciblefluid through the radiator (86) and direct contact heat exchanger (56);and, c. selectively directing flow of the water component from thecoolant loop (18) directly through the radiator (86) and back to thecoolant loop (18) by-passing the direct contact heat exchanger (56). 12.The method of claim 11, comprising the further steps of restricting flowof the water immiscible fluid from the direct contact heat exchanger(56) and the radiator loop (84) into the coolant loop (18) whenever thewater component is directed to flow directly from the coolant loop (18)to the radiator (86) and back to the coolant loop (18) by-passing thedirect contact heat exchanger (56).
 13. The method of claim 11,comprising the further step of directing flow of the water componentfrom the coolant loop (18) through the radiator (86) and back to thecoolant loop (18) by-passing the direct contact heat exchanger (56)whenever an ambient temperature is greater than thirty degrees Celsius.14. The method of claim 11, comprising the further step of turning offthe radiator pump (92) during the step of selectively directing flow ofthe water component from the coolant loop (18) directly through theradiator (86).
 15. A freeze tolerant fuel cell power plant forgenerating an electrical current from hydrogen containing reducing fluidfuel and oxygen containing oxidant reactant streams, the plantcomprising: a. at least one fuel cell (12) including a coolant inlet(14) and a coolant outlet (16) for directing a water immiscible fluidand a water component to flow through the fuel cell (12); b. a coolantloop (18) including a freeze tolerant accumulator means (22) secured influid communication with the fuel cell coolant outlet (16) for storingand separating the water immiscible fluid and the water component, adirect contact heat exchanger (56) secured in fluid communication withthe accumulator means (22) and the fuel cell coolant inlet (14), and acoolant circulating means (21) secured in fluid communication with acoolant passage (20) of the coolant loop (18) for circulating the waterimmiscible fluid and the water component through the coolant loop (18);c. a radiator loop (84) including a radiator (86) secured in fluidcommunication between a water immiscible fluid discharge (91) and waterimmiscible fluid inlet (90) of the direct contact heat exchanger (56)that removes heat from the water immiscible fluid passing through theradiator (86), and a radiator pump (92) secured to the radiator loop(84) for circulating the water immiscible fluid through the radiator(86) and direct contact heat exchanger (56); and, d. a direct contactheat exchanger by-pass system means (200) for directing flow of thewater component from the coolant loop (18) through the radiator (86) andback to the coolant loop (18) by-passing the direct contact heatexchanger (56), the direct contact heat exchanger by-pass system means(200) comprising a by-pass valve means for directing the water componentto flow from the coolant loop (18) through a by-pass feed line (201) tothe radiator (86) and from the radiator (86) through a by-pass returnline (202) back to the coolant loop (18) by-passing the direct contactheat exchanger (56).
 16. The freeze tolerant fuel cell power plant (10)of claim 15, wherein the direct contact heat exchanger by-pass systemmeans (200) further comprises water immiscible fluid isolation valvemeans for restricting flow of the water immiscible fluid from the directcontact heat exchanger (56) and the radiator loop (84) into the coolantloop (18) whenever the by-pass valve means are directing flow of thewater component directly from the coolant loop (18) to the radiator (86)and back to the coolant loop (18) by-passing the direct contact heatexchanger (56).
 17. The freeze tolerant fuel cell power plant (10) ofclaim 15, wherein the by-pass valve means comprises a coolant loopby-pass feed valve (204) for selectively directing flow of the watercomponent from the coolant loop (18) into the by-pass feed line (201), adirect contact heat exchanger feed valve (54) and direct contact heatexchanger by-pass valve (83) for selectively prohibiting flow of thewater component into the direct contact heat exchanger (56), and aradiator loop by-pass valve (206) for selectively directing the watercomponent discharged out of the radiator (86) into the by-pass returnline (202).
 18. The freeze tolerant fuel cell power plant (10) of claim16, wherein the water immiscible fluid isolation valve means comprises adirect contact heat exchanger discharge valve (208) secured in fluidcommunication with an outlet of the direct contact heat exchanger (56)for selectively prohibiting flow of the water component out of the heatexchanger (56), and a radiator inlet valve (210) secured in fluidcommunication between the by-pass feed line (201), the direct contactheat exchanger (56) and the radiator (86) for selectively directing flowfrom either the by-pass feed line (201) or the heat exchanger (56) intothe radiator (86).